The present invention relates to an anti-slip shoe sole.
Japanese Utility Model Unexamined Publication No. 62-21904 discloses a shoe sole which is formed by mixing glass fibers in unvulcanized rubber, rolling the mixture into sheets in which the glass fibers are oriented in the rolling direction, stacking a suitable number of the thus formed sheets cutting the stack of sheets in a plane perpendicular to the rolling direction so as to form anti-slip pieces, and embedding the anti-slip pieces in the ground contact surface of the shoe sole so that the cut surfaces of the anti-slip pieces will come into contact with the ground. The shoe sole produced through this process exhibits a superior anti-slip characteristic by virtue of the fact that the glass fibers dispersed in the material of the anti-slip pieces extend perpendicularly to the ground surface. Unfortunately, however, this type of shoe sole is expensive to manufacture because the anti-slip pieces require many production process steps as described and because laborious work is necessary for embedding the anti-slip pieces in the shoe sole.
A process for forming a shoe sole is also known which employs a shoe-sole forming die provided in the bottom surface thereof with a plurality of projection forming cavities. An unvulcanized green rubber having fibers of hard material such as glass fibers dispersed therein is placed in the die, and pressure and heat are applied to the rubber so as to fill the cavities with portions of the rubber and to vulcanize the same, whereby a shoe sole having a plurality of anti-slip projections is formed. This type of shoe sole suffers from the following disadvantages. When the unvulcanized green rubber is forced into the projection-forming cavities of the die, portions of the green rubber and air are confined in the cavities to flow in random directions so that the fibers in the green rubber filling the projection-forming cavities are oriented irregularly and at random. Therefore, the fibers of the hard material dispered in the anti-slip projections of the shoe sole thus formed does not produce any appreciable antislip effect.